This invention relates to gamma irradiation plant for irradiating objects or materials for the purpose of changing their biological, physical or chemical properties. Conventional gamma irradiation plant comprises irradiation equipment, shields and storage rooms, as well as equipment used for and in connection with handling and storage. Such plant is preferentially used for the sterilization of medical articles, animal feed and food for human consumption.
If, as is the case in the great majority of such installations, cobalt-60 is used as the radiation source, the gamma irradiation equipment should satisfy the following requirements:
A. It should be capable of reliable automatic operation.
B. The utilization of the available radiation should be good.
C. Irradiation should be as uniform as possible.
D. Personnel requirements should be a minimum.
E. The conditions of irradiation should be flexible.
F. The prime cost (total investment cost for the entire plant) should be low.
G. The necessary floor space should be a minimum.
With a view to satisfying these several demands gamma irradiation plant has already been proposed in which the radiation equipment comprises a plate-shaped radiation source across which the packaged goods, packed for instance in cardboard boxes, can be repeatedly traversed in several straight line paths. Outside the irradiation chamber the goods are transferred to or picked up by live roller beds. The size of the irradiated unit depends principally upon the average packing density and upon the required overdose factor, due allowance being made for an acceptable utilization of the available radiation. The overdose factor is the ratio of the greatest to the smallest radiation dose within any one irradiated unit, for instance inside a cardboard box.
In gamma irradiation plant for sterilizing medical supplies in the case of which the packing density is for example 0.2g/cc, the following are typical wording data: Irradiation unit (size of cardboard box) about 0.1 cub.m. (0.45 .times. 0.5 .times. 0.45 m), overdose factor about 1.3, and radiation utilization between 27% and 34%. Even for handling medium throughputs in the order of 1 cub.m. per hour automatic weekend operation requires several hundred meters of live roller beds and associated feeders. This equipment must be available for both the goods that have already been treated and those awaiting irradiation. Nevertheless such gamma irradiation installations are very labor intensive because the goods before and after irradiation must be manually placed on and later removed from the roller beds, consignments for different addresses must be sorted out, assembled and, for the purpose of economical further handling, they must often be stacked and secured on pallets. Empty pallets must also be handled and intermediately stored. In such gamma irradiation plants the cost of labor and staff may well exceed the cost attributable to the radioactive radiation source. Also a large storage room with assembled handling units (pallets) must be continuously made available for despatch and reception. The expenditure in means for two complete goods handling systems (one inside the irradiation chamber and one in the store) and the necessarily large floor space occupied by the store which may vary from a few hundred to several thousand square meters usually also exceed the outlay attributable to the radiation source.